Volatile organic compound emissions from a multi-unit residential building to ambient air

Emerging sources, such as volatile chemical products (VCPs) and other non-traditional emission categories, are becoming increasingly important in urban air pollution as the contributions of recognized sources such as traffic and industrial emissions decline. Indoor emissions constitute a large fraction of organic gaseous species from these sources, making buildings potential contributors to ambient air pollution. This study illustrates building emissions by presenting findings from a sampling campaign in downtown Toronto, analyzing volatile organic compounds (VOCs) from the mechanical ventilation inlet and exhaust air streams of a multi-unit residential building (110 units). Due to indoor emissions, VOCs were detected more frequently and at higher concentrations (median levels higher by about 22%) in the exhaust stream than in the inlet stream, indicating that the building serves as a net VOC source to the ambient air. VCP-related species were consistently more abundant in the exhaust air, confirming the influence of indoor sources. In particular, median concentrations of volatile methyl siloxanes and monoterpenoids associated with emissions from adhesives, personal care products, and cleaning agents ranged from about 2-5 μg m^-3 in the exhaust stream in comparison with 0.2-0.5 μg m^-3 within the inlet stream. Source apportionment analysis of VOC concentrations across the exhaust and inlet airstreams revealed indoor emissions of siloxanes, monoterpenoids, and oxygenated VOCs from coatings, cleaners, and personal care products as primary contributors to exhaust stream trends. Net building VOC emissions, defined as the rate of outflowing minus the inflowing VOCs, were calculated from the measured concentrations and ventilation rates. The resulting values aligned with indoor emissions predicted from a published VCP emission inventory for Canada, emphasizing the pivotal impact of VCP indoor sources on urban air quality. Exhaust and inlet stream concentrations of VCP-related species were found to be significantly (<i>p</i> < 0.05) correlated, suggesting the building emissions influencing outdoor VOC levels. These results highlight the crucial impact of indoor emissions, especially from VCPs, on ambient air quality and the need for further research into indoor-to-outdoor pollutant transfer mechanisms to address urban air pollution.